Control method for high-quality DC (direct current)/AC (alternating current) converter of grid-connected photovoltaic power system

Abstract

The invention provides a control method for a high-quality DC (direct current)/AC (alternating current) converter of a grid-connected photovoltaic power system, belongs to the grid-connected photovoltaic power technology, and aims to develop a high-quality DC/AC converter suitable for grid-connected operation. The control method is characterized in that a phase-shifting transformer grid connection mode is adopted, current distribution and control are performed on three-phase bridge inverters (3 and 4) according to specific conversion laws of the formula (1) and the formula (2), thyristor controllability is realized, a multi-level synthetic technology adopting equal-increment step-shaped triangular-wave current waveform is adopted, a current waveform similar to a sine wave is obtained at an output side of the phase-shifting transformer, the functions of low harmonic control, lead-lag continuous adjustment of a power factor and free regulation of direct current in the range ranging from 0 to a rated value are realized, and the method is applied to grid-connected photovoltaic power systems with various capacities.

Description

technical field [0001] The invention belongs to photovoltaic power grid-connected technology. Background technique [0002] One of the core technologies of photovoltaic power generation grid-connected system is DC / AC converter, usually called inverter. When the first photovoltaic power generation device came out in the 1980s, it used thyristor inverters, but since the 1990s, photovoltaic inverters have all used fully-controlled switching devices. Applied research on inverters has disappeared from scientific publications. [0003] The main switching devices of inverters in the current grid-connected photovoltaic power generation system use power field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and gate commutation Thyristor (IGCT), etc., the control method adopts pulse width modulation (PWM), etc., and the topology adopts voltage source inverter and current source inverter. [0004] At present, the types of sm...

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Problems solved by technology

[0004] At present, the types of small-scale photovoltaic converters less than 6kW are relatively complicated. They are basically single-phase systems without a transformer structure. There are problems such as DC current injection, leakage current generated by common-mode voltage, and large harmonics to varying degrees, so it is difficult to connect to the grid.

The construction methods of 6-100kW medium-sized photovoltaic converters also have diversified characteristics. There are both single-phase systems and three-phase systems, or three-phase systems combined with single-phase systems; there are both transformer-less structures and transformer output systems; The system without a transformer st

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